Use of var in function

why do we use var , when we can simply write a function with name myConcat

var myConcat = function(arr1, arr2) {

  "use strict";

  return arr1.concat(arr2);


Probably because the lesson or challenge you took that code from is specifically teaching you a specific form of functions called function expression stored inside variables. There are tons of ways to create and declare functions and this is just one of those.